The present invention relates to optical power limiting devices, and in particular, to a laser power limiter employing a plasma generating material comprising a particulate coated surface.
Radiation sensors are adapted to sense radiation over a wide band of wavelengths including infrared and visible light. Sensors are used for mapping, targeting, and the like. It is desirable that the sensors have high sensitivity. However, this sensitivity simultaneously renders the sensor susceptible to damage or destruction from threat radiation such as a high power laser beam directed at the sensor. The most important type of threat radiation is a short pulse, high peak power pulsed laser operating in the visible or infrared wavelength regions. Laser power limiters or "optical fuses" are used to protect sensors from such threat radiation.
At the present time, the two most significant laser power limiters are a gas plasma shutter which operates at infrared wavelengths and a liquid-particulate limiter which operates at visible wavelengths. Both of these devices respond to incident laser radiation and produce a plasma interposed between the incident radiation and a sensor. The plasma blocks the radiation by means of reflection, absorption, and diffraction. However, the gas plasma shutter cannot be used in the visible light region because the gas plasma densities produced by the device are not high enough to attenuate visible light. The liquid-particulate limiter is ineffective for use in the infrared region because no liquid has been found that effectively transmits infrared radiation. Both devices require relatively high turn-on thresholds and exhibit a variable probability of turn-on. The liquid-particulate limiter also cannot handle multi-pulse (high repetition rate) threats without implementation of a complicated means of stirring the fluid. Particulate clumping and dissolution are further problems of the liquid-particulate limiter.
Another laser power limiter device is a gas plasma switch based on the use of particulate plasma formation in a gas. This device, however, although quite useful, has a relatively high turn-on threshold, has a relatively low probability of switching, and is only suitable for use with infrared radiation.
Thus, there has heretofore existed a need for an improved radiation limiter that provides low insertion loss, wide wavelength coverage, fast rise time, multi-pulse protection, high attenuation, and fast recovery times.